HYDROLOGY OP NEW YORK 



411 



Geologically the main Mohawk lies largely in the Hudson river 

 shales and schists. The tributaries to the north flow across the 

 Trenton limestone into the unclassified granites and gneisses of 

 the Adirondack region. To the south the tributaries flow across 

 the Hamilton shales and upper and lower Helderberg groups. The 

 headwaters of Schoharie creek — the principal tributary — lie in 

 the Catskill group. 



Discharge measurements of East Canada Creel:. This gaging 

 station is located at the masonry dam of the Dolgeville Electric 

 Light & Power Company, about seven miles from the mouth of 

 the stream. Readings of the depth on the crest are taken twice 

 a day and the mean used in computing the discharge. As at the 

 other stations herein discussed, a record is also kept of the run 

 of the water wheels and the elevation of water in the tailrace. 



The dam is of rubble masonry, 19 feet high, and has a flat crest 

 6 feet wide. It is 190.25 feet long between the abutments. The 

 following cut shows a section of this dam : 



K- 6.o' 



Fig. 31 Section of dam on East Canada creek at Dolgeville. 



